Vacuum furnace and work cart for use therein

ABSTRACT

A high vacuum electric furnace for heat treating metallic articles having a work cart mounted for movement therein and including a heating chamber for receiving said work cart during the heat treating operation, said work cart having heat shielding means fixed thereto, and roller assembles located in said furnace over which said work cart moves for transfer to and from said heating chamber.

United States Patent Westeren et al.

Feb. 27, 1973 VACUUM FURNACE AND WORK CART FOR USE THEREIN Inventors: Herbert W. Westeren, Barrington; William H. Kimball, Providence; Vincent Scotto, Warwick; Wallace S. Vanderford, Jr., Coventry, all of RI.

Assignee: C. I. Hayes Inc., Cranston, R.l.

Filed: Nov. 12, 1971 Appl. No.: 163,057

Related U.S. Application Data Division of Ser. No. 770,779, Oct. 25, 1968, Pat. No. 3,599,946.

U.S. Cl ..266/5 R, 266/4 A, 266/4 B Int. Cl. ..C2ld 1/12 Field of Search ..266/4 R, 4 A, 4 B, 5 R, 6 R

[56] References Cited UNITED STATES PATENTS 3,441,452 4/1969 Westeren ..266/4 A Primary ExaminerGerald A. Dost AttorneySalter & Michaelson [57] ABSTRACT 9 Claims, 12 Drawing Figures INVgNTORS STE EN &

ATTORNEYS PATENTEBFEBZYIQB SHEET 2 [IF 6 PATENTEDFEB271975 3,718,324

' SHEET (If 6 INVEN HERBERT W. WESTEREN WILLIAM H. KM ALL VINCENT SC T O WQYLLACE S. VANDERFORD,JR. M t W ATTORNEYS PATENTED FEB 2 71973 SHEET 5 BF 6 FIG.|O

INVENTORS ESTEREN MTBALL ERFORD, JR.

FIG-.9

ATT jQRNEYS PATENTED FEB 2 7 I973 SHEET 8 0F 6 INVENTORS MI. WESTEREN F l G. l l

HERBERT WILLIAM KIMBALL VINCENT OT T8 W I X LLACE VAN M 1 M ATTORNEYS VACUUM FURNACE AND WORK CART FOR USE THEREIN BACKGROUND OF THE INVENTION The present invention relates to furnaces for heat treating metallic articles.

In the heat treatment of metallic articles, such as carbon and stainless steels and the like, it is critical in certain conditions of use thereof that the surfaces of the articles be maintained free from contamination that results from oxidation and/or decarborization. The technique employed for heat treating articles heretofore has normally consisted of heat treating in a subatmospheric environment and then moving the articles to a cooling zone through which a cooling atmosphere was circulated. Although cooling in an atmosphere was effective in certain heat treating procedures, proper hardening of certain materials could not be obtained by atmosphere cooling since this procedure required a relatively long quench cycle and the desired metallurgical structure necessitated a quick quench.

As described in US. Pat. No. 3,441,452, the technique of quenching the heat treated article in a liquid, such as oil, provided for dumping of the heat treated articles from a transfer zone into an oil quench tank located directly below the transfer zone. Although the prior techniques of quenching in oil under vacuum as disclosed in the above noted patent resulted in the desired hardening and bright surface, the dumping process was usable only with certain small articles and could not be employed for machined parts SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for vacuum heat treating metallic articles and provides for extracting of the heat treated articles from a heating zone after the heating cycle for movement to a transfer zone at which they are located on an elevator. With the heat treated parts mounted on the elevator in positive relation, the elevator is then quickly moved downwardly from the transfer zone to a quench zone at which the quenching operation is carried out in a liquid, such as oil. Since the metallic articles are retained in a fixed position on the elevator as they are moved to the quench zone, a great variety of relatively large articles can be oil quenched without risk of mechanical damage, which would normally occur in a dump quench operation.

In carrying out the invention, a unique transfer mechanism is employed for retracting a work cart, on which the articles are contained, from the heating zone to the elevator. The retracting mechanism which, in effect, tethers the work cart, cooperates with the means for operating the elevator so that the work cart is retained in a fixed position on the elevator as it is moved therewith from the transfer zone to the quench zone during the quenching operation. Since it is necessary to quickly move the articles into the quench liquid, means are further provided for controlling the rate of descent of the elevator so that as it approaches the surface of the quench liquid, it is caused to rapidly descend therethrough. The movement of the elevator is then controlled so that after it moves substantially through the quench liquid, it is caused to move to a lower position in the quench tank without shock, and then after the quenching operation is completed, the elevator is moved upwardly to the transfer zone for removal of the articles from the furnace.

Quenching of the heat treated articles is carried out by the elevator mechanism of the present invention by rapid transfer of the articles from the transfer zone to the quench tank, thus insuring that rapid quenching of the articles is achieved. Since the articles are continuously exposed to a subatmospheric environment prior to introduction thereof into the quench liquid contained in the quench tank, surface contamination of the articles is prevented, and an unusually clean and bright surface on the articles is obtained.

The vacuum furnace as embodied herein is essentially concerned with the heat treatment of articles under vacuum and transfer of the heat treated articles to a quench tank without removal of the articles from within the vacuum vessel. However, in order to obtain the results as set forth hereinafter, various constructional features, including a unique transfer elevator, are embodied in the vacuum furnace that provide for the efficient operation thereof, and such features and constructions are described hereinafter.

Accordingly, it is an object of the invention to provide a high vacuum furnace for heat treating and quenching metallic articles in such a manner as to prevent contamination of the surfaces thereof.

Another object of the invention is to provide a high vacuum electric furnace in which articles to be heat treated are moved within the furnace by remotely controlled means for automatic transfer from the heating zone to a transfer zone and thereafter into a quenching zone.

Still another object is to provide a control mechanism for withdrawing a work cart on which the articles are located from the heating zone to a transfer zone, the control mechanism including a device for locking the work cart on the elevator when the elevator is moved into the quench zone for the quenching of the articles therein.

Still another object is to provide means for controlling the vertical movement of an elevator such that the articles are rapidly moved to the quenching medi um for the quick quenching thereof.

Still another object is to provide a unique cooling system for the housing of the furnace which includes means for continuously circulating a cooling fluid in circular relation around an inner shell of the housing.

Other objects, features and advantages of the invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

FIG. 1 is a vertical sectional view of the high vacuum electric furnace embodied in the present invention;

FIG. 2 is a horizontal sectional view of the vacuum furnace illustrated in FIG. 1;

FIG. 3 is a sectional view taken along lines 3-3 in FIG. 1;

FIG. 3a is a sectional view taken along lines 3a -3a in FIG. 1;

FIG. 4 is a fragmentary sectional view of a portion of the furnace showing the control device that is employed for retracting the work cart from the heating zone to the transfer zone;

FIG. 5 is a perspective view of an end of the work cart and showing the interconnection thereof to a tape that is operable to retract the cart from the heating zone;

FIG. 6 is a fragmentary side elevational view of the work cart showing the heat shields that are associated therewith;

FIG. 7 is a partial end view, with portions shown in section, of the heat shields that are illustrated in FIG. 6;

FIG. 8 is a perspective view, showing the elevator lite mechanism and the retract mechanism for the work cart that retains the cart on the elevator in locked relation;

FIG. 9 is a side elevational view of the furnace showing the exterior piping for the cooling system;

FIG. 10 is an end elevational view of the furnace housing with portions broken away showing the circulation of the cooling fluid in the cooling space as defined between theinner and outer shells of the housing; and

FIG. 11 is a diagrammatic view showing the elevator as located in the quench zone and the system for controlling the vertical movement of the elevator within the quench zone.

DESCRIPTION OF THE INVENTION Referring now to the drawings and more particularly to FIGS. 1, 2 and 3, the vacuum furnace embodied in the present invention is illustrated and is generally indicated at 10. Since the vacuum furnace 10 is operated at a predetermined vacuum, any suitable vacuum equipment may be connected thereto for evacuating the interior thereof as required, and as illustrated in FIG. 3 as a vacuum pipe 11 is fixed in the furnace housing and communicates with a vacuum pump (not shown). As illustrated in FIGS. l-3, the vacuum furnace 10 includes a housing generally indicated at 12 that is defined by an outer shell 14, an inner shell 16 to which an end wall 18 is fixed and on which a door 20 is removably mounted. The removable door 20 is slidable on suitable tracks (not shown) and is movable transverse to the longitudinal axis of the furnace to expose the furnace interior when a work load is introduced therein or removed therefrom after a heat treating operation.

As will be described hereinafter, the outer shell 14 of the housing 12 that surrounds the inner shell 16 is substantially rectangular in cross section as compared to the circular cross section of the inner shell 16, the spacing between the inner and outer shells defining a cooling space through which a cooling fluid, such as water, is continuously circulated for maintaining the temperature of the housing walls at a prescribed level. As further illustrated in FIG. 1, both the door 20 and end wall 18 are jacketed to receive a cooling fluid therein for maintaining these parts at the prescribed temperature level.

The furnace 10 is of such size as to require a substantial support therefor, and, accordingly, spaced transverse beams indicated at 22, 24 and 26 and longitudinal beams 27 and 29 are positioned beneath the outer shell 14 for supporting the furnace thereon. The beams 22, 24, 26, 27 and 29 may be fixed in a flooring or the like or located in any suitable manner. As will be further described, the housing 12 includes a quench zone into which the heat treated articles are moved during the quenching operation. Since the quench zone must be located remote from the heating zone and if the housing 12 is mounted directly on a flooring, a suitable cavity must be formed in the flooring for receiving the quench tank as illustrated in FIG. 1 and as will be further described.

Located within the housing 12 and adjacent to the door 20 is a transfer zone 28, while located adjacent to the transfer zone 28 is a heating zone 30. The articles to be heat treated are moved into the transfer zone 28 prior to introduction thereof into the heating zone 30, and following the heating cycle the articles are returned to the transfer zone for movement therefrom into a quench zone 31 that is located directly below the transfer zone 28. As shown more clearly in FIG. 1, the heating zone 30 includes an enclosed heating chamber 32 that is defined by a casing formed of flexible insulating graphite material. The graphite insulating material is arranged in layers and, as shown in FIGS. 1, 2 and 3 includes a top wall 34, a bottom wall 36, side walls 37 and 38, a rear wall 39, and a front wall 40 in which an opening 42 is formed. Located within the heating chamber 32 are a plurality of tubular resistance heating elements 44 that are disposed in spaced relation and are interconnected at the ends thereof to suitable terminals 46. As described in US. Pat. No. 3,525,795 issued Aug. 25, 1970, and entitled ELECTRIC FUR- NACE AND TUBULAR HEATING ELEMENT FOR USE TI-IEREWITI-I, the tubular heating elements 44 are formed of a flexible woven graphite material and are arranged in tubular formation, the terminals 46 of the tubular heating elements being fixed to bus bars 48 that extend exteriorly of the furnace housing 16 through connections (not shown) for communication with a suitable source of current. Upper hanger brackets 50 and lower support brackets 52 are fixed in the heating zone for mounting the insulating walls of the heating chamber 32 in place.

Located within the heating zone 30 and fixed to the inner shell 16 of the housing 12 are a plurality of spaced roller supports 54 on which rollers 56 are mounted. The rollers 56 are rotatable in suitable bearings that are positioned in the supports 54; and, as will be described, the rollers 56 are provided for receiving a work pedestal or cart that is moved into the furnace housing during the heating cycle. In order to fix the supports 54 within the heating zone, a plurality of plates 58 are joined to the shell 16 and receive the supports 54in secure relation thereon.

After the heating cycle has been completed and the work load removed from the heating chamber 32, it is desirable to seal the heating chamber so as to effectively retain the heat therein during the cooling and quenching cycles. In order to seal the heating chamber 32, a door 60 is pivotally mounted on the front wall 40 of the chamber and, as illustrated in FIG. 1, the door 60 also includes a plurality of insulating layers that preferably are formed of a graphite material. In order to automatically control the movement of the door 60 exteriorly of the furnace, a metal tape 62 is connected to the door 60 and extends over a pulley 64 and through a tube 66 at the bottommost portion of which the pulley 64 is mounted. The tube 66 extends through a vacuum seal 68 that spans the inner and outer shells of the housing, and the tape 62 that extends through the seal 68 is operatingly connected to a piston rod 70 of a control cylinder that is preferably operated exteriorly As will be described when the work load is moved out of the heating chamber 32 following the heating cycle, the door 60 is automatically closed by the control cylinder to effectively retain the heat within the heating chamber 32.

As previously mentioned, the door is movable to an open position during unloading or loading of the articles to be heat treated. With the door 20 in an open position, a basket is placed on a work pedestal or cart generally indicated at 72, which, as shown in FIG. 1, is located in the transfer zone 28 on an elevator generally indicated at 74. As will be described hereinafter, the elevator 74 is adapted to move the work cart 72 and articles thereon to the quench zone 31 below the transfer zone 28, but, for the purpose of moving the work cart and the articles thereon to the heating zone 30, the elevator 74 is disposed in the uppermost position thereof, as illustrated in full lines in FIG. 1.

As shown in FIG. 2, the cart 72 is essentially a threesided construction and is defined by spaced channel shaped side members 78 and 80 and an end member 82. As illustrated in FIG. 7, the side members 78 and 80 have a reversely formed channel configuration that receive the rollers 56 therein, the rollers 56 thus defining tracks over which the cart 72 is moved between the transfer zone 28 and the heating zone 30. Interconnecting the side members 78 and 80 are a plurality of spaced bars 84 that are preferably formed of a molybdenum material, the outer ends of the molybdenum bars 84 being received in convenient vertical slots formed in the sides 78 and 80 and being locked in place therein by outer flanges, as indicated at 86 and 88 in FIGS. 2 and 6.

Since the width of the cart 72 is greater than the width of the heating chamber 32 as defined by the walls 37 and 38, the side members 78 and 80 extend outwardly of the heating chamber walls 37 and 38. In order to accommodate the bars 84 that support the work basket and load thereon, the walls 37 and 38 are formed with slots, as indicated at 90 and 92 in FIG. 3. Referring now to FIGS. 6 and 7, a portion of the work cart is illustrated as it is located in the heating chamber 32, the bars 84 extending through the slots 90 and 92 formed in the walls 37 and 38 respectively. Since considerable heat can escape through the slots 90 and 92 during the heating cycle, a heat shield assembly is provided that effectively shields the heating chamber 32 for retaining the heat therein. As shown in FIGS. 6 and 7, a plurality of outer heat shields 94 are joined to the side members 78 and 80 through brackets 96 that may be welded to the upper surfaces of the side members, each of the outer shields 94 being spaced between the bars 84. An end plate 97 is joined to the end most of the outer shields 94 and defines an end barrier. Fixed to the outer shields 94 and spaced therefrom for location within the slots 90 and 92 are spaced inner shields 98 and 100, the inner shields 98 and 100 being located between spacer tubes 102 and 104 and being fixed in position by a bolt 106 on which a nut 108 is received. It is seen that the outer shield 94 and the inner shields 98 and effectively prevent heat radiation through the slots 90 and 92 when the cart 72 is located within the heating chamber 32 during the heating cycle.

In carrying out the heat treating of the metallic articles within the furnace 10, the present invention provides for quick quenching of the heat treated articles in the quenching zone 31 after completion of the heat treating cycle. As shown more clearly in FIG. 1, the quenching zone 31 is defined by a quench tank 1 10 that is located within a jacket 112 through which a cooling fluid is continuously circulated. The quench tank 110 is disposed directly below the transfer zone 28, and it is contemplated that in the installation of the furnace 10, the quench tank 1 10 will be located below floor level so as to properly accommodate the quench tank with respect to the transfer zone 28 and heating zone 30. In this connection the height of the quench tank 110 is arranged such that the quench medium, which is preferably oil, is disposed at a sufficient level below the transfer zone 28. Thus, during the quenching cycle, any vaporization of the oil will be effectively trapped at the upper level of the quench tank, and contamination of the transfer zone and heating chamber will be effectively prevented. In order to condense any vaporized oil molecules and to prevent contamination of the transfer zone and heating zone, the upper level of the quench tank is enveloped by the jacket 112 for circulation of the cooling fluid therebetween, wherein the upper portion of the quench zone is effectively cooled. Purifying the quench medium and aiding in the cooling action is also produced by agitation of the quench medium by opposed impellers 114 and 116 that are located within the quench tank adjacent to the side walls thereof. As shown in FIG. 3, the impeller 114 is driven by a motor 1 18 supported from the housing support beam 27 located exteriorly of the quench tank 110, while the impeller 116 is driven by a motor 120 supported from the beam 29. Suitable seals 119 and 121 are provided for receiving the impeller shafts that are interconnected to the motors 118 and 120.

As previously described, the elevator 74 is provided for moving the work cart 72 and the articles as contained in a basket thereon into the quench zone 76 for the quick quenching of the articles following the heating cycle. As shown in FIGS. 1 and 2, the elevator 74 is defined by a frame that includes spaced front frame members 122 and 124 that are interconnected by bracing elements 126 and 128, side frame members 130 and 132, and a rear frame member 134. Joined to the frame members 124 and 134 are elongated supports 136 and 138 on which a plurality of vertical roller brackets 140 are mounted for supporting rollers 142 thereon. Fixed within the transfer zone 28 by upper brackets 143 and 145 and extending downwardly within the quench tank 110 are spaced channel shaped tracks 144 and 146. Followers 148 and are received within the tracks 144 and 146 and are operatively joined to the frame members 130 and 132 of the elevator frame. Thus,

movement of the elevator will be substantially vertical.

as the followers 148 and 150 are guided within the tracks 144 and 146.

In order to vertically move the elevator 74 with the work cart 72 mounted thereon, a hydraulic lift is employed and, as shown in FIG. 1, includes a cylinder 152 that is mounted within the quench tank 110 on a sup port bracket 154. A first ram 156 is telescopically received within the cylinder 152, the first ram 156 receiving a second ram 158 in telescoping relation therein. Joined to the topmost ram 148 is a cross head 160 on which spaced sprocket wheels 162 and 164 are fixed. Chains 166 and 167 are secured at the lower end of the cylinder at 168 and 169 respectively, and extend around the sprocket wheels 162 and 164 and are joined to links 170 and 171 (FIG. fixed to the elevator 74 on the front frame member 122. It is seen that upon actuation of the hydraulic lift, the rams 156 and 158 will be vertically moved to operate the chains 166 and 167 for moving the elevator 74 in a corresponding direction. Because the lift moves vertically as the pulleys are rotated on the cross head 160 at 2:1 mechanical advantage for movement of the elevator is obtained. Since the guide followers 148 and 150 are disposed for movement within the tracks 144 and 146, the elevator 74 must move in a prescribed vertical direction between the transfer zone 28 and the quench zone 76 upon operation of the hydraulic lift. As will be described hereinafter in the operation of the furnace, the fluid medium for operating the hydraulic lift is the quench liquid as contained in the quench tank 110. By utilizing the quench liquid for the lift cylinder, contamination of the quench zone by a hydraulic fluid as contained in an exterior system is avoided. It is for this reason that the lift cylinder 152 is mounted within the quench tank 110 as illustrated in FIG. 1.

When the work cart 72 is introduced into the furnace at the transfer zone 28 and thereafter moved into the heating zone 30, it is necessary to provide for automatically retracting the work cart onto the elevator 74 so that the elevator may then be lowered into the quench zone 76 for the quick quenching of the heat treated articles. As illustrated in FIGS. 5 and 8, a tethering and locking device that is automatically operable externally of the furnace is provided andis adapted to be interconnected to the cart 72 for retracting it from the heating zone 30. The tethering and retracting device includes an elongated metal tape 172 that is wound on a reel 174, the reel 174 being mounted on a shaft 176 that is journalled for rotation in bearings 178 and 180 that are conveniently mounted on a bracket 181 located within the transfer zone 28. As shown in FIG. 4, the shaft 176 extends outwardly of the furnace housing through a seal 182 and has a pinion 183 mounted on the outermost end thereof that is engageable by a rack 184. The rack 184 is connected to a piston rod 185 that is reciprocally moved by an automatic control device for effecting rotation of the shaft 176 and movement of the tape 172 as required.

The tape 172 as it extends from the reel 174 is received on a movable idler 182 and extends over a fixed idler 183 that is journalled between spaced plates 184 and 186 that are fixed to the frame 122 of the elevator. As shown in FIG. 4, the idler 182 is interconnected to the cross head 160 through a bracket 187, the idler 182 moving with the cross head 160 and relative to the elevator. Thus as the lift descends the elevator that is connected to the chains 166, 167 is lowered at a more rapid rate. The tape 172 is maintained in tensioned relation during this movement since it will be taken up by the vertical position of the idler 182. In order to tether and lock the work cart 72 on the elevator 74, the end member 82 of the cart is formed with holes through which the legs 188 of a U-shaped rod 190 extend (FIG. 5), the legs 188 also being received, in suitable openings formed in brackets 192 and 194 that are secured to the end member 82. The free end of the tape 172 is locked around a pin 196, shown in FIG. 8, and the pin 196 is located between the legs 188 of the rod 190 and the brackets 192, 194. It is seen that as the tape 172 is retracted onto the reel 174, the pin 196 will engage the brackets 192 and 194 and will cause the cart 72 to follow the movement of the tape 172. When the work cart reaches the fully retracted position in the transfer zone 28, the pin 196 is received at stop points indicated at 198 and 200 on the plates 184 and 186 and the cart is then located in the locked position on the elevator 74 and will be retained therein by the fully wound tape on the reel 174. It is seen that in the fully retracted position and with the elevator 74 located in the transfer zone 28, the idler 182 is at its uppermost position. As the hydraulic lift lowers the work cart 72 within the quench zone 31, the idler 182 will move downwardly with the cross head 160, tensioning the tape 172 during the downward travel of the elevator, thereby retaining the work cart 72 in its fully locked and tethered position. Thus, when the work cart reaches the quench zone 31 on the elevator 74, it will be locked in position by the tape 172 and the articles as contained thereon will be suitably positioned on the cart during the quenching operation. It is further seen that movement of the cart 72 over the elevator and through the door opening can be accomplished following the complete heat treating cycle by lifting the rod 190 from its position in the member 82. Since the cart is then essentially released from the tape 172 it may be pulled over the elevator plates 184, 186 and reel 174 and through the door opening.

During the quenching cycle and upon movement of the elevator 74 into the quench zone 31, it is essential that the elevator and articles thereon be moved rapidly into the quench liquid. However, the elevator cannot fall too rapidly from the upper position in the transfer zone 28 or splashing will occur that will contaminate the furnace interior. As will be described in the operation of the apparatus, a special control system is provided for slowly dropping the elevator to just above the quench liquid and then rapidly moving the elevator into the quench liquid. This control system includes an actuating arm 202 that is mounted on the elevator 74 and extends thereabove, the actuating arm 202 being adapted to engage an operating element of a control valve for effecting the control of the system that provides the intended movement of the elevator.

Prior to the instant invention the housings of vacuum furnaces have usually been constructed of a stainless steel material, which, in large installations, is relatively costly. In the present invention the use of stainless steel in the furnace housing is avoided by forming the housing inner shell 16 of a mild steel and then applying a thin Teflon coating to the outer surface of the inner shell 16. The Teflon coating not only prevents corrosion of the inner shell which is normally subjected to water circulation therearound but effectively reduces the overall cost of the furnace construction. Protection of the vacuum vessel walls as represented by the inner shell 16 is also contemplated by chemically treating the circulating coolingliquid. This would effectively resist corrosion. Further, the use of a heat exchanger in the cooling system would reduce the corrosive activity of the cooling fluid on the inner shell. If desired, the outer jacket 14 may also be formed of a mild steel.

It has been the usual practice in cold wall vessels of the general type embodied in the present invention to enclose a cylindrical inner shell in a cylindrical outer shell and circulate a cooling medium therebetween. However, circulating the cooling medium between the cylindrical shells heretofore has been relatively inefficient, since the temperature of the inner shell could not be easily controlled because of the poor circulation of the cooling fluid. In order to adequately cool all of the surfaces of the furnace as embodied in the present invention, a large flow of cooling liquid is required. This is accomplished by enclosing the inner shell 16 with the outer shell 14 that has a substantially rectangular configuration in vertical cross section as illustrated in FIG. 10. The outer shell 14 is open at the top to further provide for effective cooling of the circulating fluid, the fluid being directed in a circulating flow around the inner shell 16. For this purpose, a plurality of jets 206 are located along the length of the outer shell 14 and introduce the cooling fluid under pressure into the cooling space between the inner and outer shells 14 and 16. As shown in FIGS. 9 and 10, the cooling system includes a pump 208 that supplies the jets 206 with the cooling fluid, such as water, and receives a continuous flow of the cooling fluid through a pipe 210 that communicates with the outer shell adjacent to the upper end thereof. As seen in FIG. 10, the jets 206 are located substantially tangential to the inner shell 16; and thus, upon injecting of the cooling fluid into the cooling space, a circulating action of the cooling fluid is produced, as indicated by the arrows in FIG. 10. It is also seen that suction of the water through the pipe 210 by the pump 208 further induces the circulating action of the cooling fluid. In the event that the temperature of the cooling fluid in the cooling space exceeds a prescribed level, fluid such as water can be added through a supply pipe 212, as indicated in FIG. 9, and an inlet pipe 214 that communicates with the cooling space adjacent to the upper end thereof. In the event that excess cooling water is introduced into the cooling space, a drain 216 is provided for draining the excess as required.

As shown in FIG. 12, the cooling system also provides for introducing the cooling fluid to the various areas of the furnace that require cooling. Thus, a pipe 218 supplies the cooling fluid to the cooling space between the quench tank 110 and the jacket 112. Pipe 220 provides the necessary cooling fluid for the end wall 18. The bus bars 48 are water cooled, and convenient flexible tubing 222 is connected to the bus bars 48 for conducting the cooling fluid thereto. Additional pipes 224 and 226 connected to the supply pipe 212 are also provided for conducting the cooling fluid to the jacketed space in the door 20. A flexible hose 227 that is interconnected to the pipes 224 and 226 enables the door to be shifted laterally during loading or unloading of the furnace.

As mentioned above, the inner shell 16 is formed of mild steel and has a thin Teflon coating applied thereto. In order to visually inspect the inner shell 16, the outer shell 14 has a plurality of inspection ports 219 located in the side walls thereof, as indicated in dotted lines in FIG. 1. As shown in FIG. 3a, an annular flange 221 surrounds each of the ports 219 and receives a cover plate 223 thereagainst in sealing relation. Sealing dogs 225 are bolted to the flange 221 and engage the cover plate 223 for locking it in sealing engagement against the flange 221. It is seen that after the cooling fluid is removed from the cooling space between the shells, the cover plates 223 may be removed to uncover the ports 219, whereupon the inner shell 16 may then be visually inspected.

OPERATION In operation of the furnace 10 as embodied herein, a work load is first placed in a convenient basket or receptacle, and the work load as contained in the basket is placed on a transfer table (not shown) as it is located outside the furnace. With the door 20 open, the transfer table is rolled adjacent thereto, and the basket and work load thereon are moved therefrom onto the cart 72 as it is located on the elevator 74 in the transfer zone 28. The work cart 72 is then moved into the heating zone 30, wherein the work basket and the articles to be heat treated as contained therein are located within the heating chamber 32. The door 20 is closed and sealed and the furnace evacuated for the heating cycle. Since the transfer zone 28, heating zone 30 and quench zone 76 are all in open communication, all of these zones are evacuated by the vacuum pump equipment during the heat treating cycle. It is understood that when the work cart 72 is moved into the heating zone 30 as illustrated in FIG. 2, the tape 172 has been interconnected therewith, and is unwound from the reel 174 as illustrated in FIG. 2. The cycle of operation is then automatic as will now be described. After the heating cycle has been completed, the pump valve intercom necting the furnace and vacuum pump is closed. The furnace is then back-filled with nitrogen to a desired subatmospheric pressure, preferably about 12 in. hg and the oil circulating pumps 114, 116 are started. When the transfer chamber 28 reaches the desired backfill pressure, the control cylinder for the door 60 is actuated to cause the door to be moved to the open position, as illustrated in FIG. 1. The cylinder operating the rack 184 is next actuated and the reel 174 is rotated by the pinion 183 to retract the tape 172, thereby withdrawing the work cart 72 and basket thereon into the transfer zone 28. As the cart 72 is withdrawn from the heating zone, the side members 78 and 80 are received on the rollers 142 of the elevator 74. When the tape 172 is fully retracted, the work cart 72 is disposed in tethered and locked position on the elevator 74. The door 60 is now returned to the closed position and the apparatus is ready for the quenching cycle.

Referring now to FIG. 11, a diagrammatic illustration of the system for controlling the operation of the hydraulic lift is illustrated, and movement of the elevator during the quenching cycle will now be described. When the work cart reaches the transfer zone and is located on the elevator, a solenoid operated three-way valve 228 is energized to locate the actuating portion of the lift cylinder 152 in communication with the interior of the quench zone 31 by way of lines 230, 232, 234 and 236. As the hydraulic fluid bleeds out of the cylinder 152 into the quench tank 110, the elevator slowly descends. As previously mentioned, it is desirable to move the heat treated articles through the surface of the quench liquid very rapidly so as to effect a quick quenching thereof, and thereby prevent vaporization of the quenching medium. In order to accomplish this purpose, the operating arm 202 moves into engagement with the operating element of the control valve 238. The control valve 238 is then placed in communication with the line 234 by way of line 240. The operating fluid that is bleeding from the cylinder 152 into the quench tank 1 by way of line 236 is now further exhausted into the quench tank through the line 240, valve 238 and a bleed valve 242. The elevator then quickly descends through the surface of the quench medium and drops substantially into the quench tank. As the operating arm 202 passes over the actuating element of the valve 238, this valve is then once more closed to prevent the operating fluid from exhausting into the quench tank 76. The elevator then slowly descends to the bottom of the quench tank without undue shock as the elevator reaches the bottom of the tracks 144 and 146.

After a predetermined period for quenching of the articles within the quench zone, the three-way solenoid valve 228 is automatically activated to place the exhaust of a pump 246, mechanically interconnected to an air operated motor 244, into communication with the line 232. The operating fluid is now pumped from the quench tank into the cylinder 152 by way of line 236, control valve 250, line 252, exhaust line 254, and line 232. Since the pump 246 draws the fluid through the lines 236 and 252, and because the head pressure in the quench tank keeps the pump supplied, the fluid will not enter line 240 or valve 238 as the actuating arm 202 engages the valve element of valve 238 upon upward movement of the elevator. As the operating fluid enters line 232 and into the bottom of the cylinder 152, the hydraulic lift is moved upwardly through the quench zone 76 and back into the transfer zone 28. A bleed valve 256 to which a line 258 is connected and that communicates with the interior of the quench zone is provided for bleeding the hydraulic system as required.

As previously described, a cooling gas may be introduced into the transfer zone 28 and circulated therein, and for this purpose a cooling fan 260 is provided that circulates the cooling gas prior to the quenching of heat treated articles in the quench zone 76.

It is seen that the system as described herein is completely automatic; and, once the heat treating cycle has begun with the work cart 72 located in the heating zone 30, the operation thereafter is carried out at predetermined intervals, wherein the heat treated articles are moved into the transfer zone 28, thereafter moved into the quench zone 76, and, after the quenching operation, are moved upwardly and returned to the transfer zone 28 for removal from the furnace. By rapidly removing the articles from the heating zone and quenching in the manner as illustrated and described, the surfaces of the articles being heat treated are effectively protected and the desired metallurgical properties are attained with minimal distortion of the articles. Protection is further assured by heat treating the articles under vacuum and transferring the articles to the quench zone without removal of the article from the vacuum environment. This technique of heating under vacuum and rapidly quenching prevents contamination from occurring on the surfaces of the articles and further provides the articles with an unusually bright-appearing surface.

It is understood that the vacuum furnace as described herein is preferably operated to maintain the furnace interior and quench zone at a subatmospheric pressure even during quenching. However it is contemplated that after evacuating the furnace to remove the contaminants and impurities therefrom, the heating zone, transfer zone and the area above the quench liquid can be backfilled with a suitable atmosphere so that the heat treating and quenching operations are carried out at partial pressures or even at positive pressures. Thus even though the heat treating, cooling and quench cycles could be carried out in positive pressures with respect to atmosphere, the furnace interior must still be evacuated initially and the unit would still be designated as a vacuum furnace.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

What is claimed is: V

l. A vacuum furnace construction, comprising a housing having a heating zone and a transfer zone located in adjacent relation, a work cart mounted for movement in said housing to and from said heating and transfer zones, means located in said zones on which said work cart is moved, said heating zone including insulating side walls in which horizontal slots are formed through which a portion of said work cart extends when it is moved into said heating zone, and means secured to said cart for shielding the slots to prevent heat loss therethrough when the work cart is located in said heating zone.

2. A vacuum furnace construction as set forth in claim 1, said work cart being defined by a u-shaped frame having parallel legs, said means on which work cart is moved including a plurality of rollers mounted in fixed position in said housing in horizontal spaced relation, each of the legs of the work cart having a channel configuration for receiving said rollers therein and for facilitating movement of said work cart.

3 A vacuum furnace construction as set forth in claim 2, said work cart having a plurality of cross bars interconnected to said legs for receiving a work basket thereon, said cross bars defining the portion of the work cart that extends through said slots in the insulating side walls of said heating zone.

4. A vacuum furnace as set forth in claim 3, said shielding means including a plurality of heat shields fixed to the legs of said work cart and being disposed in shielding position relative to the slots in the insulating side walls of said heating zone when said work cart is located therein.

5. A vacuum furnace as set forth in claim 4, said heat shields including outer elements spaced inwardly of said work cart legs and outwardly of said insulating side walls, and inner elements being spaced inwardly of said outer elements and being receivable in said slots when said work cart is located in said heating zone.

6. A vacuum furnace as set forth in claim 1, said work cart including side legs that are normally located exteriorly of the insulating side walls when the work cart is positioned in said heating zone, cross bars interconnecting said legs and extending through the slots in said side walls, said shielding means being interconnected to said side legs for shielding said slots.

7. A vacuum furnace as set forth in claim 6, said shielding means including a plurality of heat shields that are plate-like in conformation and that are positioned in spaced, parallel relation.

8. A vacuum furnace as set forth in claim 7, a first set of heat shields located exteriorly of the side walls of said heating zone in adjacent relation to said slots.

9. A vacuum furnace as set forth in claim 8, a second set of heat shields interconnected to said legs and being disposed inwardly of said first set of heat shields and being receivable in the slots in the side walls of said heating zone when the work cart is located therein, wherein radiation of heat through said slots is effectively prevented during a heat treating operation. 

1. A vacuum furnace construction, comprising a housing having a heating zone and a transfer zone located in adjacent relation, a work cart mounted for movement in said housing to anD from said heating and transfer zones, means located in said zones on which said work cart is moved, said heating zone including insulating side walls in which horizontal slots are formed through which a portion of said work cart extends when it is moved into said heating zone, and means secured to said cart for shielding the slots to prevent heat loss therethrough when the work cart is located in said heating zone.
 2. A vacuum furnace construction as set forth in claim 1, said work cart being defined by a u-shaped frame having parallel legs, said means on which work cart is moved including a plurality of rollers mounted in fixed position in said housing in horizontal spaced relation, each of the legs of the work cart having a channel configuration for receiving said rollers therein and for facilitating movement of said work cart.
 3. A vacuum furnace construction as set forth in claim 2, said work cart having a plurality of cross bars interconnected to said legs for receiving a work basket thereon, said cross bars defining the portion of the work cart that extends through said slots in the insulating side walls of said heating zone.
 4. A vacuum furnace as set forth in claim 3, said shielding means including a plurality of heat shields fixed to the legs of said work cart and being disposed in shielding position relative to the slots in the insulating side walls of said heating zone when said work cart is located therein.
 5. A vacuum furnace as set forth in claim 4, said heat shields including outer elements spaced inwardly of said work cart legs and outwardly of said insulating side walls, and inner elements being spaced inwardly of said outer elements and being receivable in said slots when said work cart is located in said heating zone.
 6. A vacuum furnace as set forth in claim 1, said work cart including side legs that are normally located exteriorly of the insulating side walls when the work cart is positioned in said heating zone, cross bars interconnecting said legs and extending through the slots in said side walls, said shielding means being interconnected to said side legs for shielding said slots.
 7. A vacuum furnace as set forth in claim 6, said shielding means including a plurality of heat shields that are plate-like in conformation and that are positioned in spaced, parallel relation.
 8. A vacuum furnace as set forth in claim 7, a first set of heat shields located exteriorly of the side walls of said heating zone in adjacent relation to said slots.
 9. A vacuum furnace as set forth in claim 8, a second set of heat shields interconnected to said legs and being disposed inwardly of said first set of heat shields and being receivable in the slots in the side walls of said heating zone when the work cart is located therein, wherein radiation of heat through said slots is effectively prevented during a heat treating operation. 